When an analog to digital converter is not converting an analog input to a digital output, it usually consumes about the same amount of power as when it is converting. In some systems, the analog to digital converter may be shut down when not needed to convert analog signals to digital signals. When a conversion is needed, it can take time to turn the analog to digital converter back on. This time is referred to as a startup time, and prevents use of an analog to digital converter circuit immediately after it is turned back on. When switched capacitor circuits are used, the startup times may last several clock cycles until the analog to digital converter reaches a proper working area.
In battery powered devices, the analog to digital converter may consume significant current even when the device is not being actively used. Still, the analog to digital converter is either left on and ready for conversion, or is turned off. Leaving it on may consume significant battery power. Turning it off, may lead to undesirable delays in using the device while the analog to digital converter is turned back on.